1. Field of the Invention
The present invention relates to an apparatus for driving an imaging device which is provided in a digital camera and the like to convert an object image to an electrical image signal.
2. Description of the Related Art
Conventionally, in an imaging device (i.e., CCD) of a full frame transfer type, which is provided in an electronic endoscope, a light receiving element is formed by a vertical transfer CCD, which functions both as an accumulating unit, in which an electric charge generated in the light receiving element is accumulated, and a vertical transfer passage, through which the electric charge is transferred. In the light receiving element, a plurality of electrodes are provided. During an exposure period in which the light receiving elements are exposed, a control signal for controlling the light receiving elements is supplied to each of the electrodes, so that a potential well is formed in each of the light receiving elements (i.e., the accumulating unit) in accordance with the control signal, and an electric charge, generated due to an opto-electric conversion of each of the light receiving elements, is accumulated in the potential well. In an output period of an image signal, the accumulated electric charge is transferred to a horizontal transfer CCD through the light receiving elements (i.e., the vertical transfer passage), and output from the horizontal transfer CCD to outside.
When a temperature of air surrounding the CCD becomes high, or when an accumulating period of the electric charge becomes long, a dark current occurs in the light receiving elements, and thus, unwanted electric charges are generated in the light receiving elements. In such a case, in the CCD of the full frame transfer type, the unwanted electric charges generated in a light receiving element flow into light adjacent light receiving, so that a smear occurs, which may cause the quality of an image signal to deteriorate.